A good search function with many options is simply a must! And it's something that really should be achievable. Like how many days old (good for curators), minimum views, maybe recommendations to posts similar to what you liked previously. Minimum post size would be nice too, anything that makes finding decent posts easier. Having certain people I follow to show up first when they post.
I'd love to have infinite time on posts but it's less likely to happen :) also I keep pdf backup version of all my posts as I've noticed some images dissapear from older posts which is a pitty. Having 10 day post payout would maybe be doable :)